Improvement in expansion-valves for steam-engines



Patented Dec; 9, 1879.

I n-venorz N. PB'ERS. PHDTO LITNOGRAFHEE WASHINGTON. D Q

3 3 is a plan view of plate B. Fig. 4 is' a dlagra-m, showingthe crank or eccentric K.

' toward or away from one another, in order to crank or eccentric, placed at K, Fig. 4:, diaits travel until after the closing of the said,

- being short and narrow, thetravel of the slide UNITED S A-res PATENT OFF CE.

ALEXIS BRETONNEAU, FILS,OF MORTAGNE-SUR-SEVRE, FRANCE.

IMPROVEMENT 'lN EXPANSION-VALVES FOR STEAM-ENGYINESJ- Specifi bation forming part of Letters Patent No. 222.376, dated December 9, 1879; applicationiiledf October To all whom t't may concern:

Be it known that I, ALEXIS BRETONNEAU, fils,o tf Mortagne-sur-Sevre, have invented Im provements in Expansion-Valves for Steam- Engines; and I do hereby declare that the followingis a full, clear, and exact description of the same, reference being had to the annexed sheet'of drawings, making a part of the same.

This invention relates to an improved system of variable expansion-valve for steam-ch gines, and is illustrated in the accompanying Figure 1 is a vertical section of a steam-chest Fig. 2 is a horizontal section of the steam-chest.

The invention consists ofan expansion slidevalve, A, Figs. 1 and 2, on the back of the main slide-valve D, and of two movable cutofi plates, 0 O, on the back of the expansionvalve A, which do not participate in the 1110-. tion of the slide-valve, but may be adjusted nearer or farther apart from one another by means of studs g g, each engagingin a curved slot in a plate, B, (shown separately in Fig. 3,) on turning which the slides G O are moved out oft earlier or later, and so vary the grade of expansion. A spring, y,presses lightly on the back of the plates 0 O, to keep them close against the expansion-valve A, and the latter against the main slide D.

The expansion-valve A is actuated by a metrically opposite the driving-crank of the engine, if the latter runs both ways, or at K, a little in advance of thisposition, if it runs one way only, in order that the expansionvalve A'shall be moving at a certain velocity when the cylinder-ports are uncovered by the main valve, and shall not arrive at the end of ports, in order to avoid wiredrawing bythe. plates 0 O at the beginning and end of the stroke. The two slide-valvesD and A move independently, and the travel of the valve A depends on the space available in each case. Thus, in the example shown, the valve-chest thesmallestpossible diameter,passing through astuffing-box in the cover of the valve-chest, and is operated by a governor or hand-lever. In order to set out the slots in plate B for the studs g, I mark on the line a a, Fig. 3,beginning at a point, 1, a little below linem m, the

positions of the plate 0, which correspond: at

the cut-off to one of the regular points of division of the piston-stroke (tenths, forinstance) by the points 1, 2, 3, &c., and from these points, with o as a center, I describe arcs whose intersection with the radii o, 0 0 &c.,- give the center line of the curve for the slot which is to operate the plate O. For the other slot I proceed in the same way for the divisions of the line a n but instead of radii I draw tangents n a a &c., to lines which, like do, each pass through a point of the first curve and tangentially to a circle, 0 0, described with the radius 0 a. This gives two curves differin g in proportion to the varying efl'ect upon the piston due to the length of the connectingrod and of the eccentric-rod of a valve.

The operation is as follows: When the pis- "EOlI is at the commencement of its stroke and the crank is at H, Fig. 4, the crank or eccentrio operating valve A is at K, and the edge 4 of the port 2 is in line with the axis of plate B, so that if the plates 0 C were brought quite close together the port 2 would .not be uncovered at all, so that steam would not be admitted to the main valve, and the cut-ofl' would then be at the very beginning of the stroke. Supposing the plates 0' G to be eseparated each for the distance y, Fig. 4, corresponding to the travel of the expansion-valve A during the uncovering of the cylinder-port by the main valve, the expan sion-valve A would have to move thisdistance y before the edge 4: of port 2 would close the port, which would take place at the moment when the main valve closes the cylinder- A is only one-tenth of that of the main valve port, and the cut-off will then be-atth'e end of the stroke of the main valve, supposing it to be without lap. The intermediate position of the plates C 0' correspond to grades of expansion between these two extremes.

The apparatus is easily controlled directly by a governor, the power required to turn plate B being very small. It works without shock, there being no stop, and is consequently applicable to engines running at high speeds as well as engines running both ways. By placin g the eccentric or crank which operates the expansion-valve A diametrically opposite to the driving-crank, this expansion-valve is in position for rotation either way of the crankshaft, and it is only necessary to operate the main valve in order to reverse the engine, the expansion-valve being left to the control of the governor, if one be employed, whereby the elastic force of the steam is utilized to the greatest possible extent. The governor holding the plates 0 at their greatest distance apart when the engine is stopped enables it to be started again in either direction with full pressure, whereby irregularities and difficulties are avoided at the moment of starting, and the engine can be worked as if it had an ordinary D-valve, which are very important advantages.

I am aware that slide-valves have already been combined with expansion-valves, covers thereto, and slotted regulating-plates. This I do not claim but in all previous arrangements the slots in the regulating-plates were either alike, which is a serious error, or constructed so as to give an equal movement to the two plates.

I claim The combination of the slide-valve D and sliding expansion-valve A with the plates 0 0, pins 9 g, spring y, slotted plate,B, which has two curved slots of different form, said slots being formed, the one on radii o, 0 &c., the other on tangential lines a a, 850., so that by the motion of the plate B the position of the plates 0 O is .varied in proportion to the varying efl'ect upon the piston due to the length of the connecting-rod and of the cocentric-rod of a valve, as and for the purpose set forth.

ALEXIS BRETONNEAU, FILS.

Witnesses:

GEORGE GIFFORD,

U. 5'. Com. Agent. G. BRAUR. 

